Joint implants, also referred to as joint prostheses, joint prosthetic implants, joint replacements, or prosthetic joints, are long-term surgically implantable devices that are used to partially or totally replace diseased or damaged joints, such as a hip, a knee, a shoulder, an ankle, or an elbow, within the musculoskeletal system of a human or an animal. Since their first introduction into clinical practice in the 1960s, joint implants have improved the quality of life of many patients. Both artificial hip joints and artificial shoulder joints are generally ball and socket joints, designed to match as closely as possible the function of the natural joint. Generally, the artificial socket is implanted in one bone, and the artificial ball articulates in the socket. A stem structure attached to the ball is implanted in another of the patient's bones, securing the ball in position.
The ball and socket joint of the human hip unites the femur to the pelvis, wherein the ball-shaped head of the femur is positioned within a socket-shaped acetabulum of the pelvis. The head of the femur or ball fits into the acetabulum, forming a joint which allows the leg to move forward, backward, and sideways in a wide range. The acetabulum is lined with cartilage, which cushions the bones and allows the joint to rotate smoothly and with minimal friction. An envelope of tough ligaments connects the pelvis and femur, covering the joint and stabilizing it. Cartilage also makes the joint strong enough to support the weight of the upper body and resilient enough to absorb the impact of exercise and activity. A healthy hip allows the leg to move freely within its range of motion while supporting the upper body and absorbing the impact that accompanies certain activities.
Various degenerative diseases and injuries may necessitate replacement of all or a portion of a hip using synthetic materials. Prosthetic components are generally made from metals, ceramics, or plastics, or combinations of them.
Total hip arthroplasty and hemi-arthroplasty are two procedures well known within the medical profession for replacing all or part of a patient's hip. These procedures have enabled hundreds of thousands of people to live fuller, more active lives. A total hip arthroplasty replaces both the femoral component and the acetabular surface of the joint, and so both a femoral prosthesis and an acetabular prosthesis are required. A hemi-arthroplasty may replace either the femoral component or the acetabular surface of the joint. The purpose of hip replacement surgery is to remove the damaged and worn parts of the hip and replace them with artificial parts, called prostheses, with the purpose of at least partially restoring the hip's function, including but not limited to, restoring the stability, strength, range of motion, and flexibility of the joint.
In total hip replacement surgery, commonly referred to as total hip arthroplasty, a patient's natural hip is replaced by two main components: an acetabular cup component that replaces the acetabular socket, and the femoral component, or the stem-and-ball component, that replaces the femoral head.
A conventional acetabular cup component may include a cup, a cup and a liner, or in some cases only a liner, all of which may be formed in various shapes and sizes. Generally, a metal cup and a polymeric liner are used. However, the liner may be made of a variety of materials, including polyethylene, ultra high molecular weight polyethylene, and ceramic materials. The cup is usually of generally hemispherical shape and features an outer, convex surface and an inner, concave surface that is adapted to receive a cup liner. The liner fits inside the cup and has a convex and concave surface. The cup liner is the bearing element in the acetabular component assembly. The convex surface of the liner corresponds to the inner concave surface of the cup or acetabulum, and the liner concave surface receives the head of a femoral component. An acetabular cup may include a highly polished inner surface to decrease wear.
The femoral or stem-and-ball component of the hip prosthesis generally includes a spherical or near-spherical head attached to an elongate stem, with a neck connecting the head and stem. In use, the elongate stem is located in the intramedullary canal of the femur, and the spherical or near-spherical head articulates relative to the acetabular component. Femoral prostheses used in total hip arthroplasty procedures may or may not differ from an endoprosthesis used in a hemi-arthroplasty. The femoral head of each type prosthesis is generally a standard size and shape. Various cups, liners, shells, stems and other components may be provided in each type arthroplasty to form modular prostheses to restore function of the hip joint.
During a total hip replacement, the surgeon will take a number of measurements to ensure proper prosthesis selection, limb length, and hip rotation. After making the incision, the surgeon works between the large hip muscles to gain access to the joint. The femur is pushed out of the socket, exposing the joint cavity. The deteriorated femoral head is removed.
In order to install the acetabular cup, the surgeon prepares the bone by reaming the acetabular socket to create a surface for accepting a cup. The cup may be held in place by bone cement or an interference or press fit, or it may have a porous outer surface suitable for bony ingrowth. The new acetabular shell is implanted securely within the prepared hemispherical socket. The plastic inner portion of the implant is placed within the metal shell and fixed into place.
Next, the femur is prepared to receive the stem. The proximal end of the femur is at least partially resected to expose the central portion of the bone. Generally, at least part of the greater femoral trochanter is resected to gain access to the central portion of the femur, specifically, the medullary canal. In the central portion, a cavity is created that matches the shape of the implant stem, utilizing the existing medullary canal. The top end of the femur is planed and smoothed so that the stem can be inserted flush with the bone surface. If the ball is a separate piece, the proper size is selected and attached. Finally, the ball is seated within the cup so that the joint is properly aligned, and the incision is closed.
During shoulder replacement, the ball and socket joint of the human shoulder is replaced with a prosthetic joint using a procedure similar to that described above. During a shoulder replacement operation, at least a portion of the proximal section of the humeral shaft is replaced by a metal prosthesis. This prosthesis generally consists of two parts: a stem that is mounted into the medullary canal of the humerus, and a head component connected in some manner to the stem. The head component replaces the bearing surface of the humerus and articulates within the glenoid cavity of the scapula to allow movement of the shoulder.
An arthritic humeral head (ball of the joint) may be removed and replaced with a humeral prosthesis. If the glenoid socket is unaffected, a hemiarthroplasty may be performed (which means that only the ball is replaced). The humeral component is made of metal and is usually press fit, but sometimes cemented, into the shaft of the hone of the humerus.
If the glenoid is affected, but conditions do not favor the insertion of a glenoid component, a non-prosthetic glenoid arthroplasty may be performed along with a humeral hemiarthroplasty. In this procedure, the humeral prosthesis is installed, and the patient's glenoid shape and orientation are corrected to articulate the humeral prosthesis, for example, by reshaping the socket by reaming. The prosthetic ball of the humeral component then articulates with the reshaped bony socket of the glenoid. In a total shoulder joint replacement, or total humeral arthroplasty, the glenoid bone is shaped by reaming and oriented, and then covered with a prosthetic glenoid component that is commonly stabilized by bone cement.
During joint replacement surgery, such as the procedures described above, a rather large incision is typically required to allow the surgeon adequate access to the joint. The large incision is needed to properly use the instruments needed to prepare the bones for installation of the prosthetic joint components and to install the prosthesis itself For example, during total hip replacement surgery, some conventional surgical techniques generally require an approximately 25 to 35 cm incision in the lateral (side) or posterior (back) aspect of the patient for installing, respectively, the acetabular component and the femoral component of the prosthetic hip. Other conventional surgical techniques include two smaller incisions: a first, anterior incision to install the acetabular member; and the second, posterior incision to install the femoral component. In this technique, both the first and the second incisions are approximately 3 cm to approximately 5 cm in length. The two-incision technique is considered advantageous over the one incision technique because it minimizes the trauma to the patient and results in quicker and better patient rehabilitation than the technique involving a longer incision. Currently available data suggests that the longer incision, either posterior or lateral, increases patient morbidity. Thus, for joint replacement surgery, particularly for hip replacement surgery, it is desirable to reduce the size and the number of the incisions without jeopardizing surgical access to the joint.
Patient positioning during hip arthroplasty is important for surgical access, proper preparation of the joint, and installation of the prosthetic components. Both initial positioning of the patient for the surgery and maintenance of the patient's position throughout the surgery are essential. Various approaches to improving patient positioning exist. For example, some of the conventional hip arthroplasty techniques use supine (on the back) positioning of the patient, with an operating or surgical table including a dropping part on one side of the lower end. This allows the lowering of the patient's operative leg for increased access to the proximal femur.
During recent years, an effort has been made to reduce the size of the incision needed to implant joint prostheses through so-called “minimally invasive” surgery (“MIS”). The term “minimally invasive surgery” generally refers to the surgical techniques that minimize the size of the surgical incision and trauma to tissues, and are generally less intrusive than conventional surgery, thereby shortening both surgical time and recovery time. Minimally invasive arthroplasty techniques are advantageous over conventional arthroplasty techniques by providing, for example, a smaller incision, less soft-tissue exposure, improved ligament balancing, and minimal trauma to the muscle and ligament mechanisms. To achieve the above goals of MIS, it is necessary to modify traditional implants, instruments, and surgical techniques to decrease the length and number of the surgical cuts, as well as to decrease the exposure of and trauma to the internal joint structures. The benefits of MIS surgery can be significant, at least partially because smaller and fewer incisions and the less intrusive nature of the procedure shorten both surgical time and recovery time. Thus, it is advantageous to modify traditional implants, instruments, and methods to make them particularly suitable for use in minimally invasive surgical procedures.
Another recent development in joint replacement is computer-assisted or computer-aided surgical (CAS) systems that use various imaging and tracking devices and combine the image information with computer algorithms to track the position of the patient's leg, the implant, and the surgical instruments and to make highly individualized recommendations on the most optimal surgical cuts and prosthetic component selection and positioning. Several providers have developed and are marketing imaging systems based on CT scans and/or MRI data or on digitized points on the anatomy. Other systems align preoperative CT scans, MRIs, or other images with intraoperative patient positions. A preoperative planning system allows the surgeon to select reference points and to determine the final implant position. Intraoperatively, the system calibrates the patient position to that preoperative plan, such as by using a “point cloud” technique, and can use a robot to perform surgical procedures. Other systems use position and/or orientation tracking sensors, such as infrared sensors acting stereoscopically or otherwise, to track positions of body parts, surgery-related items such as implements, instrumentation, trial prosthetics, prosthetic components, and virtual constructs or references such as rotational axes that have been calculated and stored based on designation of bone landmarks. Processing capability such as any desired form of computer functionality, whether standalone, networked, or otherwise, takes into account the position and orientation information as to various items in the position sensing field (which may correspond generally or specifically to all, portions, or more than all of the surgical field) based on sensed position and orientation of their associated fiducials or based on stored position and/or orientation information. The processing functionality correlates this position and orientation information for each object with stored information regarding the items, such as a computerized fluoroscopic imaged file of a bone, a wire frame data file for rendering a representation of an instrumentation component, a trial prosthesis or actual prosthesis, or a computer generated file relating to a rotational axis or other virtual construct or reference. The processing functionality then displays position and orientation of these objects on a screen or monitor or otherwise. The surgeon may navigate tools, instrumentation, trial prostheses, actual prostheses and other items relative to bones and other body parts in order to perform joint replacement more accurately, efficiently, and with better alignment and stability. Instruments and surgical techniques that can be used in computer-assisted surgery are highly desirable.
It is highly desirable to adapt the surgical instruments used in preparation of the femoral bone during hip replacement to minimally invasive surgery, computer assisted surgery, or both. The instruments used in femoral preparation include, but are not limited to, osteotomes or chisels used for resecting at least a portion of the femoral head to expose the central portion of the femur, and broaches, reamers, and rasps, used to clean and enlarge the hollow center of the bone, creating a cavity that matches the shape of the femoral component's stem.
During hip replacement surgery, the surgeon opens a femoral intramedullary canal by removing a portion of the trochanteric fossa with an osteotome or a chisel, an instrument for surgical division or sectioning of bone. The surgeon then uses one or a series of increasing size cavity preparation devices, such as reamers or broaches, to prepare a cavity for installation of a femoral stem. By using a series of gradually increasing in size devices, the surgeon expands the intra-femoral cavity until the desired size and shape is created. Sometimes, the portion of the final broach inserted into the femoral cavity serves as a trial femoral stem.
For the success of hip replacement, it is generally desired to select and install the femoral stem of the largest size suitable for a particular patient. Electing the largest appropriate femoral stein helps to stabilize the femoral component in the femur, improves alignment, and reduces the potential of the femoral component's loosening and failure. There is a need for instruments and method for preparation of a femoral cavity that permit installation of an appropriately sized stem of the femoral component in order to improve alignment and stabilization of the femoral component in the patient with minimum interference the tissue of the patient.
In minimally invasive surgery, the need to insert and operate the femoral preparation instruments through smaller incisions may conflict with the proper instrument alignment needed to create the cavity of the largest possible size. For proper access and alignment, long incisions and other invasive procedures are often required. The single-incision lateral or posterior approach hip-arthroplasty procedure may simplify access to the femur, but it requires muscle dissection. The two-incision procedures, on the other hand, make approach to the femur difficult. When the anterior approach to the femur is used, muscle dissection is not necessary, but properly positioning the femur to allow access along the long axis often requires releasing the posterior hip capsule. The posterior capsule comprises a blood vessel, and surgically releasing the capsule greatly releases the risk of bleeding. The anterior approach used with some traditional instruments, such as straight femoral reamers, results in extensive trauma to the patient's tissues. Therefore, there is an unrealized need for instruments and techniques for preparation of a femoral cavity that reduce the incision size and trauma to tissues without jeopardizing preparation of the cavity of the largest appropriate size, which provide for proper sizing and alignment of the femoral component's stem, and which will improve restoration of hip function and reduce the risk of the prosthesis loosening and failing.
In summary, there is a current unrealized need for improved devices, systems and procedures adapted for use in minimally invasive surgery (MIS). There is a particular unrealized need for improved devices for preparation of a patient's femur for installing a femoral component of a hip prosthesis. Improved devices are desired that are adapted for introduction and operation through a smaller surgical incision than conventionally available devices. Also needed are improved devices, systems, and procedures that would minimize the damage to the flesh, muscle, and other soft tissues during insertion, operation, and withdrawal. At the same time, there is a need for improved devices, systems, and procedures that would improve sizing and aligning of the femoral components and reduce the risk of their loosening. Also desired are improved devices, systems, and procedures suitable for computer-assisted surgery.
In general, devices and systems are needed that are easy to use and manufacture, minimize tissue damage, simplify surgical procedures, are versatile, allow for faster healing with fewer complications, require less post-surgical immobilization, and are less costly to produce and operate.